Reservoir Rock Properties

Abdulla Ali Al-Dombi

Professor of Petroleum Engineer

https://aldambi.blogspot.com/ مدونة بالعربية

https://aldambi2.blogspot.com/ Blog in English

Introduction

Introduction

• Petroleum (crude oil) is a complex mixture consisting mainly of hydrocarbons and containing sulfur, nitrogen, oxygen, and helium as minor components.
• A natural gas is defined as a homogeneous fluid of low viscosity and density that has no definite volume but expands to completely fill the container in which it is placed.
• Generally, the natural gas is a mixture of hydrocarbon and non-hydrocarbon gases.

​

3

Introduction

• Reservoir is a natural or artificial place where water, oil, gas and mineral are collected and stored.
• Hydrocarbons are organic compounds which contain only two elements, hydrogen and carbon.
• A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations.
• The reservoir rock is porous and permeable.
• A reservoir rock is a place that oil migrates to and is held underground.

​

​

4

Cross Section Of A Petroleum System

(Foreland Basin Example)

���Classification of Reservoirs���

​

​

​

6

Reservoirs Types

Oil Reservoirs

​

Gas Reservoirs

​

​

Reservoir temperature is less than the critical temperature of the hydrocarbon fluid

​

Reservoir temperature is greater than the critical temperature of

the hydrocarbon fluid

�Classification of Oil Reservoirs�

​

​

​

7

Oil Reservoirs

Under-saturated oil reservoir

Gas-cap reservoir

Saturated oil reservoir

Oil Initial reservoir pressure > bubble point pressure

Oil Initial reservoir pressure = bubble point pressure

Oil Initial reservoir pressure < bubble-point pressure

��Classification of Gas Reservoirs��

​

​

​

​

8

�Classification of Fluids Reservoirs�

​

​

​

9

Reservoir fluids

Oil Natural gases

water systems

Crude oil systems

Dry-gas, Wet-gas, gas-condensate

Heavy black oil, Light crude oil, volatile crude oil

Low concentration,

High concentration

�Reservoir Rock Properties�

​

​

​

10

Reservoir Rock Properties

Oil Reservoir

Properties

Rock

Oil

Gas

Geological rock types Chemical rock types

Structural rock types

Porosity

Permeability

Compressibility

ROCKS

In geology, rock or stone is a naturally occurring solid aggregate of one or more minerals or mineraloids. For example, the common rock granite is a combination of the quartz, feldspar and biotite minerals.

Igneous

Sedimentary

Metamorphic

IGNEOUS ROCKS��

• Comprise 95% of the Earth's crust.
• Originated from the solidification of molten material
• Volcanic: glassy in texture due to fast cooling
• Plutonic: slow-cooling, crystalline rocks

​

METAMORPHIC ROCKS��

• Formed by the action of temperature and/or pressure on sedimentary or igneous rocks.
• Marble: formed from limestone
• Hornfels: from shale or tuff
• Gneiss: is similar to granite but formed by metamorphosis

SEDIMENTARY ROCKS��

• These are the most important for the oil industry
• They contain most of the source rocks and cap rocks
• They are split into two categories:
• Clastic
• Non-clastic or tuff

DEFINITIONS - SEDIMENTARY ROCK

CLASTIC AND CARBONATE ROCKS

SEDIMENTARY ROCK TYPES

Relative Abundances

���Cap Rock���

• A reservoir needs a cap rock.
• Impermeable cap rock keeps the fluids trapped in the reservoir.
• It must have zero permeability.
• Some examples are:
• Shales.
• Evaporites such as salt or anhyhdrite.
• Zero-porosity carbonates.

​

​

​

​

​

​

18

���Cap Rock(cont.)���

19

Petroleum Trap

• Petroleum trap, underground rock formation that blocks the movement of petroleum and causes it to accumulate in a reservoir that can be exploited.
• The oil is accompanied always by water and often by natural gas; all are confined in a porous and permeable reservoir rock.

​

​

20

Petroleum Trap(cont.)

• Many systems have been proposed for the classification of traps; one simple system divides them into:-
• Structural traps and
• Stratigraphic traps.
• The most common type of structural trap is formed by an anticline, a structure with a concave roof caused by the local deformation of the reservoir rock and the impermeable cap rock.
• In a stratigraphic trap, variations within the rock strata themselves (e.g., a change in the local porosity and permeability of the reservoir rock) play the important role.

21

Structural Traps

• In petroleum geology, a structural trap is a type of geological trap that forms as a result of changes in the structure of the subsurface, due to tectonic, gravitational and compaction processes.
• Types of Petroleum traps include:
• Anticline Trap
• Fault Trap
• Salt Dome Trap

​

​

22

Structural Traps(cont.)

• Anticline Trap
• If a permeable rock like sandstone or limestone is located between impermeable rock layers like shale and the rocks are folded into an anticline, oil and gas can move upward in the permeable reservoir rocks, and accumulate in the upper region of the anticline.

​

​

23

Structural Traps(cont.)

• Fault Trap
• If faulting can shift permeable and impermeable rocks so that the permeable rocks always have impermeable rocks above them, then an oil trap can form.
• Note that both normal faults and reverse faults can form this type of oil trap.

​

​

​

​

24

Structural Traps(cont.)

• Salt Dome Trap
• Salt in creating the domes also adds faults and fractures due to the extra pressures on the rocks. The traps around the dome are difficult to find as anything below the Salt is invisible on the surface seismic.

​

25

Reservoir Rock Properties

Abdulla Ali Al-Dombi

Professor of Petroleum Engineer

https://aldambi.blogspot.com/ مدونة بالعربية

https://aldambi2.blogspot.com/ Blog in English